This invention relates to heat stabilizers for polymers derived from halogen-containing ethylenically unsaturated compounds such as vinyl chloride and vinylidene chloride. This invention further relates to heat stabilizers for halogen-containing polymers containing an antimony or bismuth compound and a second component which synergistically improves the level of heat stability imparted by the antimony or bismuth compound.
The efficacy of certain compounds of antimony and bismuth as heat stabilizers for halogen-containing polymers such as polyvinyl chloride is well known. For example, U.S. Pat. Nos. 2,680,726; 2,684,956; 3,399,220; 3,466,261; 3,493,536; 2,161,024; 2,461,531; 2,556,420; 2,556,208; 2,801,988 and 3,530,158 disclose various sulfur- and non-sulfur-containing antimony compounds that are useful for this purpose. While these antimony compounds do impart considerable heat stability to halogen-containing polymers they have a number of disadvantages, two of the more serious ones being the tendency of many antimony compounds to exude from the polymer composition and the inherent instability of some sulfur-containing antimony compounds upon exposure to heat or light for relatively short periods of time.
In addition, antimony compounds are often more costly than other conventional heat stabilizers and do not possess any advantages in performance to balance their shortcomings. These disadvantages have delayed the commercial acceptance of antimony compounds as heat stabilizers for halogen-containing polymers.
It has now been found that the long-term stability of certain antimony and bismuth compounds and the efficacy of these compounds as heat stabilizers for halogen-containing polymers such as polyvinyl chloride can be synergistically improved by the presence of aryloxides or aromatic esters containing boron, phosphorus, silicon, antimony, tin or zinc.